The present invention is related to a system using sensor nodes that intermittently operates so as to save power by repeating activated state and inactivated state at a regular interval, more specifically to a technology for synchronization of time in the entire system.
ZigBee is a wireless communication method used in a conventional sensor network. See ZigBee standard, published by ZigBee Alliance, on the ZigBee Alliance Website (URL: http://www.zigbee.org/) (searched on May 21, 2007).
There is also a grid search method as a method of identifying the earthquake focus. For example, see the technical document on the overview and processing method of the Earthquake Early Warning (EEW), on the Japan Meteorological Agency website (URL: http://www.seisvol.kishou.go.jp/eq/EEW/kentokai5/) (searched on May 21, 2007).